The invention relates to removal of acid gases-carbon dioxide (CO2) and sulfur-containing components such as hydrogen sulfide (H2S) and carbonyl sulfide (COS) that are simply referred to as sulfur components or sulfur from a gas mixture that contains acid gases such as synthesis gas (syngas) or natural gas. In a process of acid gas removal by solvent, a specified sulfur concentration in the produced acid gas stream is required by the downstream sulfur recovery unit. To meet the sulfur specification of the acid gas stream, equipment for enriching sulfur content in the acid gas stream, such as sulfur-rich solvent flash drum(s), concentrators with product gas stripping and the combination of the two have been used in acid gas removal units. For example, in US 2013/0036911, a syngas treatment configuration having two flash drums to enrich the acid gas is provided to produce acid gas stream with 40 mol % H2S or higher as required by a Claus unit for sulfur recovery. The main concept of a re-absorber is that the sulfur content in the sulfur-rich solvent from the bottom of a sulfur absorber is concentrated by stripping off carbon dioxide with stripping gas, such as a flash gas from the overhead of a sulfur-rich solvent flash drum (rich flash gas) and nitrogen, in the bottom part of the re-absorber, which produces a CO2-rich gas (the function of a concentrator), and that the sulfur components in the CO2-rich gas is absorbed by contacting with solvent in the upper part of the re-absorber (the function of re-absorption). The advantage of a re-absorber design over the conventional sulfur-rich solvent flash drum/concentrator design is that the overhead of the re-absorber is vented or sent out as CO2 product instead of being recycled back to the sulfur absorber, which avoids the additional capital and operating costs related to the increase of throughput of the sulfur absorber and the carbon dioxide absorber if so equipped by the recycle gas from the sulfur-rich flash drum/concentrator.
This invention also relates to heat integration in a process of acid gas removal by solvent. In these types of processes, various gas streams containing carbon dioxide can have very low temperatures. The cold gas in those streams can be utilized to cool other process streams in the unit that requires low temperature, such as the lean solvent, to reduce the utilities that are required to cool the other process streams.